Stare at the center of the disk for about 15 seconds. Stare at the palm
of your hand. Notice that your palm seems to be turning in the opposite direction from the way you turned the wheel.

What's Going On?

When you stare at a moving pattern, your eyes and brain get used to seeing
movement. When you look at something that's
standing still, your eyes see movement in the opposite direction. The
common name for this illusion is the waterfall effect.
If you stare at a waterfall for some time and then look at the nearby
rocks, the rocks may look like they are moving upward.